When conveying and reading a medium in an image reading apparatus such as a scanner, a skew (oblique movement), that is, a medium being conveyed in a tilted manner, may occur and a medium region in an input image in which the medium is imaged may tilt. Such an image reading apparatus needs to execute image processing such as tilt correction processing of a medium region and cropping processing of a medium on an input image in which the medium is imaged in a tilted manner.
An image reading apparatus correcting a tilt of image data read from a regular document, based on a comparison result between read image data of a reference document an image of which is read while being conveyed with previously stored reference image data of the reference document, is disclosed (see Japanese Unexamined Patent Publication (Kokai) No. 2008-167093).